There are a number of domestic and foreign reported studies about resistivity distribution and characteristics of the silicon single crystal doped with Ga. For example, Pei, Su Hua et al. have disclosed a diffusion model and distribution principle of Ga in SiO2/Si system (see Rare Metals and Material Engineering 2005, 6, pages 920-923). They studied diffusion characteristics of Ga in SiO2/Si system and surface and particle distribution of Ga. A production process of the silicon single crystal doped with Ga was also disclosed in Japan by Abe Takao for improving resistivity distribution of silicon single crystal doped with Ga in the pulling direction and for producing silicon single crystal with more uniform resistivity. Accordingly, a method for producing silicon single crystal doped with Ga based on the CZ method was proposed in the disclosure, which called for a reduction in atmosphere pressure during growth of the silicon single crystal (see Method For Producing Ga-Doped Silicon Single Crystal, JP2002154896, 2002-05-28).
The major difficulty encountered by the pulling method (also known as the Czochralski method or CZ method) is a large resistivity difference produced between the head portion and the tail portion of the Ga-doped silicon single crystal made according to a conventional CZ pulling method. This is due to the very low segregation coefficient of Ga in Silicon (e.g. k0=0.08, while segregation coefficient of Boron in Silicon is 0.8). The ratio of resistivity of head portion to that of tail portion sometimes may reach 50-60 and therefore only a small portion of the silicon single crystal ingots produced can be utilized in solar cells.
U.S. Pat. No. 6,815,605 disclosed a method of producing silicon single crystal doped with Ga, which was aimed to solve the problem of photo-degradation in the silicone single crystal having a high oxygen concentration. However, the ingot produced by the method has a resistivity range between 5Ω·cm and 0.1Ω·cm, a 50 time difference.